Wireless communication products are being more and more diversified in the recent ten years and widely applied in daily life, and are required to be thin, aesthetic and portable to achieve convenience in usage, thus related miniaturized antenna designs are continuously proposed. The miniature antenna generally refers to an antenna having a space size much smaller than its operating wavelength, and theoretical study has pointed out that the radiation resistance of the miniaturized antenna is small with fairly low radiation efficiency.
As shown in FIG. 1, a meander line is provided which is disclosed in U.S. Pat. No. 5,892,490. The meander line includes a based member 12 and a radiation conductor 11 disposed within the base member 12 with continuous bending for resonance. In the meander line, to achieve the aim of miniaturization, the radiation conductor 11 must be bent many times and distributed densely within a smaller area, ensuring directions of electric currents being opposite in any two parallel and adjacent conductor segments 111 in the radiation conductor 11; further with more bending times, the distance between opposite electric currents formed separately in two equally adjacent and parallel conductor segments 111 is shorter, while with shorter distance between the two opposite electric currents, far-field counteraction generated by the two electric currents can be more severe, further leading to low radiation efficiency of the antenna.
When the radiation efficiency gets lower, not only unstable communications can be caused, a product adapting such antennas can also be more and more energy consuming, so electricity charging is often required, further resulting to inconvenience for users.
To design an antenna with fairly good performance at smaller space, in addition, as shown in FIG. 2, a radiation conductor of the antenna is adopted with a method such as fractal dimension extension in geometry algorithm of Hilbert curve; and representatives of such method, for example, those described in U.S. Pat. Nos. 7,148,805, 7,164,386, 7,202,822, 7,554,490, and US application publication No. US2007/0152886, and etc.
The Hilbert curve filling a plane 2 can non-interlace to pass through every split unit with equal area to form a pattern with fractal dimensions, thus theoretically, adopting such Hilbert curve as a design approach of the radiation conductor 11 can make the antenna achieve an effect of limitless miniaturization, but in fact, for the antenna applying such Hilbert curve, the increase in length of the distributed radiation conductor 11 in a specific area can make the number of conductor segments 111 which are adjacent, paired and parallel in the radiation conductor 11 increase and come closer to each other; additionally, the method of forming the radiation conductor 11 can also make electric current amplitude similar but opposite in phase for every paired conductor segments 111. When two electric currents with identical amplitude but opposite phase get closer, the two opposite electric currents counteract in far-field radiation and the resulted problem of radiation efficiency drop would be more serious, therefore in order to take into account of radiation efficiency of communications product specifications, the miniaturized method is restrained.
Additionally, features of various antennas with fractal dimension structure including Hilbert curve have been experimented and discussed in reference 1. Reference 1 illustrates that with an increase in fractal dimension and iterations number, the radiation efficiency and quality factor of antenna of the fractal dimension structure would decrease, wherein the antenna designed by Hilbert curve is the most serious, and the fixed relationship between resonance frequency and geometric dimension also restrains the degree of freedom in designing such type of antennas. Reference 1: J. M. Gonzalez and J. Romeu, “On the influence of fractal dimension on radiation efficiency and quality factor of self-resonant prefractal wire monopoles,” 2003 IEEE International Symposium on Antennas and Propagation and USNC/CNC/URSI North American Radio Science Meeting, vol. 4, pp. 214-217, June, 2003.